How to add a comment to pdf that displays in Win 10 File Explore "comment" column

Hello
As you may already know, these three metadata properties, shown in the PDF-ShellTools Info tip screenshot you attached, are not part of the PDFs metadata. These are from a metadata system, that uses a NTFS Alternate Data Stream to store the data itself, that MS introduced in Win2K. An ADS is like an additional file, usually hidden by the system, that is attached to the main file. Since Windows Vista there is no longer a Shell native way to edit these properties (the Summary file properties tab sheet no longer exists). This is also a bad method to add metadata to files that support storage of metadata in the file itself, such as the PDF. If you move these files to a media that don't use the NTFS, you will loose the metadata.
PDF-ShellTools don't provide means to manage these non-PDF native metadata properties, and Windows 7 don't use that file summary information system, so the best way to deal with this is to move that metadata to PDFs metadata properties. In your case you can move the Subject to the PDFs Subject standard metadata field, and the other to PDFs custom metadata fields.

You will need a script, such as the one I posted at this forum post, to easily do that. Let me know If you have doubts on how to adapt it to your case.

When done, the PDF-ShellTools property handler Shell extension will provide the means to show, edit and search these properties, using the powerful Windows 7 Property System, that since Windows Vista replaced that, now obsolete, file summary information system.

var WshShell = new ActiveXObject("WScript.Shell");

function setMetadata(params) {
  WshShell.Run('"%ProgramFiles%\\PDF-ShellTools\\PDFShellTools.exe" SetMetadata ' + params, 1, true);
}

var objShell = new ActiveXObject("shell.application");
var objFolder2;
objFolder2 = objShell.NameSpace(WshShell.currentdirectory);
if (objFolder2 != null) {
  var FolderItems;
  FolderItems = objFolder2.Items();
  if (FolderItems != null) {
    var FolderItem;
    var Subject;
    var Category;
    var Comments;
    for (var i = 0; i < FolderItems.count; i++) {
      FolderItem = FolderItems.item(i);
      if (FolderItem.name.split('.').pop().toLowerCase() == 'pdf') {
        Subject = objFolder2.GetDetailsOf(FolderItem, 11);
        Category = objFolder2.GetDetailsOf(FolderItem, 12);
        Comments = objFolder2.GetDetailsOf(FolderItem, 14);
        var cmd = "'Subject=" + Subject + "','Keywords=" + Category + "','Comments=" + Comments + "'";
        //WshShell.Popup(cmd, 0, FolderItem.path, 0x30);
        setMetadata("\"Metadata="+cmd+"\" \"" + FolderItem.path + '"');
      }
    }
  }
}

var WshShell = new ActiveXObject("WScript.Shell");
var objShell = new ActiveXObject("shell.application");
var objFolder2;
objFolder2 = objShell.NameSpace(WshShell.currentdirectory);
if (objFolder2 != null) {
  var msg = '';
  for (var i = 0; i < 50; i++) {
    msg += objFolder2.GetDetailsOf(objFolder2, i) + "[" + i + "]\n";
  }
  WshShell.Popup(msg, 0, "Message", 0x30);
}